Add Procfile

Add Procfile to run cube-dashboard on Heroku, or using foreman locally.
Add CUBE_REMOTE_FILE to be able to pass config file

Allow config file to be loaded from a remote URL by setting the
CUBE_REMOTE_FILE environment variable.
Allow config in DASHBOARD_CONFIG environment variable

Allow dashboard configuration to be set in a new environment variable,
DASHBOARD_CONFIG.  This allows the configuration to be kept out of
version control.
add versioned dependency for node